what form do i fill out to correct a taxable amount 2b is checked that they were unable to determine the tax amount

[xmasbaby0]

You do nothing to correct that. Enter your 1099R just as it appears and let the software calculate how much is taxable.   The financial institution that issued your 1099R does not know about your other income so they do not determine how much of your distribution is taxable.

[dmertz]

What is the code in box 7 of the Form 1099-R?

Is the IRA/SEP/SIMPLE box marked?

If the IRA/SEP/SIMPLE box is not marked, why were they unable to determine the taxable amount.

[NCperson]

@Lwadelka 

if there IRA box was not checked, is there an amount in Box 9b? if there is no amount in Box 9b, then everything is taxable.  If there is an amount in Box 9b, then post back and I can explain how to calculate what is taxable.